Over the years, Romy has experimented with using multiple tele-converters in shooting his wonderful bird images.
Tell you the truth, I haven't paid that much attention to his surfing photography.
Here is one setup that I remember.
http://www.pbase.com/liquidstone/image/59586426
He has since sold the Sigmonster and works with other lenses.
I worked for a long time in the Subic Bay, Philippines area, where Romy has done much of his photography. I never ventured into the jungle there. I don't really regret not doing so because I thought that it might be dangerous. Anyway, at the time, I was shooting film with a Canon DSLR and the longest lens I owned was 200mm.